Early roller cutter rock bits did not have ball bearings to support the cutter on the shaft. Such bits utilized rings held on the shaft by a nut and such rings were externally threaded to receive the roller cutter thereon. The axial thrust was taken by the ring against the nut in one direction and against a washer or the body in the other direction. The H. R. Hughes U.S. Pat. Nos. 979,496, 1,010,144 and 1,124,445. Such structures did not provide sealed lubrication systems for the roller cutter. Further the application of a sealed lubrication system to such prior art structures would be very difficult as it would require multiple seals.
Recent rock bit designs have utilized ball bearings between the shaft and the cutter to absorb the thrust of the cutter. With such ball bearing designs the ball races are provided in the cutters and mating races are provided in the shafts. The surfaces of these races have been made hard to avoid surface fatigue problems. Carburizing grades of steel have been used for these rock bits but such steels have been found to be subject to cracking when hard metal inserts are used. A drill bit design which did not include a ball bearing would allow the use of medium carbon, through hardening, steels and thus avoid the cracking problem when hard metal inserts are used.
In such structures the portion of the body through which the balls are loaded into their race weakens the body and the journal.